2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
26 TranspositionTable TT; // Our global transposition table
29 /// TranspositionTable::set_size() sets the size of the transposition table,
30 /// measured in megabytes. Transposition table consists of a power of 2 number
31 /// of clusters and each cluster consists of ClusterSize number of TTEntry.
33 void TranspositionTable::set_size(size_t mbSize) {
35 assert(msb((mbSize << 20) / sizeof(TTEntry)) < 32);
37 uint32_t size = ClusterSize << msb((mbSize << 20) / sizeof(TTEntry[ClusterSize]));
39 if (hashMask == size - ClusterSize)
42 hashMask = size - ClusterSize;
44 mem = calloc(size * sizeof(TTEntry) + CACHE_LINE_SIZE - 1, 1);
48 std::cerr << "Failed to allocate " << mbSize
49 << "MB for transposition table." << std::endl;
53 table = (TTEntry*)((uintptr_t(mem) + CACHE_LINE_SIZE - 1) & ~(CACHE_LINE_SIZE - 1));
57 /// TranspositionTable::clear() overwrites the entire transposition table
58 /// with zeroes. It is called whenever the table is resized, or when the
59 /// user asks the program to clear the table (from the UCI interface).
61 void TranspositionTable::clear() {
63 std::memset(table, 0, (hashMask + ClusterSize) * sizeof(TTEntry));
67 /// TranspositionTable::probe() looks up the current position in the
68 /// transposition table. Returns a pointer to the TTEntry or NULL if
69 /// position is not found.
71 const TTEntry* TranspositionTable::probe(const Key key) const {
73 const TTEntry* tte = first_entry(key);
74 uint32_t key32 = key >> 32;
76 for (unsigned i = 0; i < ClusterSize; i++, tte++)
77 if (tte->key() == key32)
84 /// TranspositionTable::store() writes a new entry containing position key and
85 /// valuable information of current position. The lowest order bits of position
86 /// key are used to decide on which cluster the position will be placed.
87 /// When a new entry is written and there are no empty entries available in cluster,
88 /// it replaces the least valuable of entries. A TTEntry t1 is considered to be
89 /// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from
90 /// a previous search, or if the depth of t1 is bigger than the depth of t2.
92 void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV, Value evalM) {
95 TTEntry *tte, *replace;
96 uint32_t key32 = key >> 32; // Use the high 32 bits as key inside the cluster
98 tte = replace = first_entry(key);
100 for (unsigned i = 0; i < ClusterSize; i++, tte++)
102 if (!tte->key() || tte->key() == key32) // Empty or overwrite old
105 m = tte->move(); // Preserve any existing ttMove
111 // Implement replace strategy
112 c1 = (replace->generation() == generation ? 2 : 0);
113 c2 = (tte->generation() == generation || tte->bound() == BOUND_EXACT ? -2 : 0);
114 c3 = (tte->depth() < replace->depth() ? 1 : 0);
116 if (c1 + c2 + c3 > 0)
120 replace->save(key32, v, b, d, m, generation, statV, evalM);